With recent rapid tends to high integration density of DRAM (Dynamic Random Access Memory) used as main memories of personal computers and work stations, there have been intensively developed dielectric and electrode materials which can realize a high integration density.
To impart predetermined dielectric characteristics to dielectric materials, a crystallization heat treatment under an oxidative atmosphere is necessary. Polysilicon, tungsten and titanium nitride have conventionally been used as the material for electrodes which is laminated with a dielectric substance. However, since the electrode is oxidized when subjected to a heat treatment at high temperature under an oxygen atmosphere, the electrode is inferior in heat resistance. Thus, intense interest has shown towards Pt which is less likely to react with oxygen at high melting point, and Ru, RuO2, Ir and IrO2 which maintain excellent electrical conductivity even when oxidized. In the formation of a film of Ru or RuO2, a sputtering method is often used. For fine working required with higher integration density, a MOCVD method has been researched.
As the MOCVD material containing Ru, for example, cyclopentadiene materials such as bis(cyclopentadienyl)ruthenium (hereinafter referred to as Ru(Cp)2) complex and bisethylcyclopentadienyl ruthenium (hereinafter referred to as Ru(EtCp)2) complex, and β-diketone materials such as tris-2,2,6,6-tetramethyl-3,5-heptadionate ruthenium (hereinafter referred to as Ru(DPM)3) complex are used.
Among these materials, the Ru(DPM)3 complex is not often used as the MOCVD feedstock because its vapor pressure is lower than that of the Ru(Cp)2 complex and Ru(EtCp)2 complex. The Ru(EtCp)2 complex has such advantages that a conventional film forming apparatus can be employed because it exists in the form of liquid at about room temperature, and the feedstock can be fed in a stable manner because its flow rate can be controlled by a conventional mass flow controller. However, the Ru(EtCp)2 complex is not easily handled because it is unstable in air. Since the Ru(Cp)2 complex exists in the form of a solid at about room temperature and does not substantially dissolve in an organic solvent, it must be fed into a film forming chamber by a sublimation method and has problems such as increase in feed amount and poor stability. However, the Ru(Cp)2 complex is easily handled because it is stable to an air.
Various studies on the formation of a film using a Ru(Cp)2 complex by the MOCVD method are reported in P. C. Liao et al. Thin Solid Films, 287, pp. 74–79 (1996), Aoyama et al. Jpn. J. Appl. Physics, 38, pp. 2194–2199 (1999), Kadoshima et al. Preliminary Manuscript of the 47th Lecture of The Japanese Society of Applied Physics, pp. 515, and Moto et al. Japanese Patent Application, First Publication No. 2001-234347. According to these studies, Ru and RuO2 films having excellent characteristics are formed by the MOCVD method that employs a solid sublimation method.
However, the principal object of the above studies on the formation of a film using the Ru(Cp)2 complex by the MOCVD method is to evaluate characteristics and the film forming method of Ru and RuO2 films, and there is no description about an influence of the content of impurities in the Ru(Cp)2 complex as the feedstock on the film formation.